Bumpless semiconductor device

ABSTRACT

When connecting a semiconductor device such as an IC chip with a circuit board by the flip-chip method, a semiconductor device is provided without forming bumps thereon, which enables highly reliable and low cost connection between the IC chip and circuit board while ensuring suppressing short-circuiting, lowering connection costs, suppressing stress concentrations at the joints and reducing damage of the IC chip or circuit board. The bumpless semiconductor device is provided with electrode pads  2  on the surface thereof and with a passivation film  3  at the periphery of the electrode pads  2 , and conductive particles  4  are metallically bonded to the electric pads  2 . Composite particles in which a metallic plating layer is formed at the surface of resin particles are employed as the conductive particles  4.  This bumpless semiconductor device can be manufactured by (a) causing conductive particles to be electrostatically adsorbed onto one face of a flat plate; and (b) overlaying the surface of the plate having the adsorbed conductive particles on the surface of electrode pads of a bumpless semiconductor device which is provided with the electrode pads on the surface thereof and with a passivation film at the periphery of the electrode pads, and ultrasonically welding this assembly, so that the conductive particles are metallically bonded and transferred from the flat plate to the electrode pads.

TECHNICAL FIELD

The present invention relates to a bumpless semiconductor device.

BACKGROUND ART

When a bare IC chip is connected to a circuit board by flip-chip method,a separation must be provided between the IC chip and the circuit boardin order to prevent occurrence of short-circuiting at scribe lines thatare not covered with passivation film. Connecting bumps of height ofabout 10 μm to 80 μm are therefore commonly formed on the IC chip (FIG.3 to FIG. 5).

In the embodiment shown in FIG. 3, the gold bumps 31 of an IC chip 32having gold bumps 31 formed by the stud bump method and a connectionterminal 34 of a circuit board 33 are thermo-compression bonded using ananisotropic conductive adhesive 37 (film or paste) obtained bydispersing conductive particles 35 in a binder 36. Also, in theembodiment shown in FIG. 4, the gold bumps 41 of an IC chip 42 havinggold bumps 41 formed by the stud bump method and a connection terminal44 of a circuit board 43 are thermo-compression bonded using aninsulating adhesive material 45 (film or paste).

It should be noted that, in the embodiments of FIG. 3 and FIG. 4, theadhesive force between the IC chip and the circuit board depends on thecoagulative force of the binder (adhesive component) in the anisotropicconductive adhesive (insulating adhesive), since there is no mutualmetallic bonding between the bumps 31 (41) and the connecting terminals34 (44).

Also, in the case of the embodiment of FIG. 5, connection of solderbumps 51 and connecting terminals 54 is achieved by bringing theflux-treated connecting terminals 54 of a circuit board 53 into contactwith the solder bumps 51 of an IC chip 52 formed with solder bumps 51 bya solder paste printing/reflow method or other method, and heating toabove the melting point of the solder, where the gap between the IC chip52 and the circuit board 53 is filled with an underfilling agent 55. Inthis case, usually, a washing operation is performed in order to removethe flux before filling with the underfilling agent 55.

However, the embodiments of FIG. 3 to FIG. 5 all presuppose theformation of bumps on the IC chip, which are costly to produce, so thereare the problems that the freedom of the IC chip shape is lowered and itis difficult to reduce the cost of effecting connection between the ICchip and the circuit board.

Since, in the embodiments of FIG. 3 and FIG. 4, no metallic bonding isachieved between the bumps 31 (41) and the connecting terminals 34 (44),the adhesive force between the IC chip and the circuit board must dependon the coagulative force of the binder (adhesive component) in theanisotropic conductive adhesive (insulating adhesive). Thus there arethe problems that reliability of connection in the case of theembodiment of FIG. 3 that employs an anisotropic conductive adhesive canbe guaranteed, but in the case of the embodiment of FIG. 4, which doesnot employ an anisotropic conductive adhesive, the reliability ofadhesion is lower than in the case of metallic bonding.

Furthermore, in the case of the embodiment of FIG. 3, withminiaturization of the bump pitch and miniaturization of the bump size,there is the problem that the risk of occurrence of short-circuiting isincreased if the content ratio of conductive particles 35 in theanisotropic conductive adhesive 37 is increased in order to ensure thepresence of such conductive particles 35 between the bumps 31 andconnecting terminal 34. A further problem is that the cost of connectionbetween the IC chip 32 and the circuit board 33 is increased due to thecomparatively high cost of procurement of the conductive particles 35.In the case of the embodiment of FIG. 4, the bumps 41 and connectingterminals 44 are directly press-fixed without interposing conductiveparticles between the bumps 41 and the connecting terminals 44, so thereis a problem of stress concentration at the joints, which further lowersconnection reliability. Also, since the pressure during press-fixingmust be high, there is a possibility of the IC chip or circuit boardsustaining comparatively large-scale damage.

On the other hand, in the case of the embodiment of FIG. 5, althoughcomparatively satisfactory connection reliability is achieved due to themetallic bonding between the solder bumps 51 and the connectingterminals 54, there is the problem that, if the bumps are madesufficiently large to ensure that metallic bonding is formed, it isdifficult to make finer the pitch of the solder bumps 51. Additionalproblems are that a flux F washing step and underfilling agent 55filling step are added.

The present invention was made in view of the above problems of theprior art. Its object is to make it possible to join an IC chip and acircuit board when connecting a semiconductor device such as a bare ICchip with a circuit board by the flip-chip method, with high reliabilityand low cost without forming bumps on the semiconductor device, whilesuppressing short-circuiting, lowering connection costs, suppressingstress concentrations at the joints and reducing damage of the IC chipor circuit board.

DISCLOSURE OF THE INVENTION

The present inventors discovered that metallic bonding of conductiveparticles exclusively with the electrode pads could be achieved by firstelectrostatically adsorbing the conductive particles on to a flat platesuch as a glass plate, followed by fixing by ultrasonic wave pressure inwhich this surface of the flat plate with conductive particles adsorbedthereon is overlaid with the surface of a semiconductor device on theside of the electrode pads, and thereby succeeded in perfecting thepresent invention.

Specifically, according to the present invention, there is provided abumpless semiconductor device comprising electrode pads provided on thesurface thereof, and a passivation film formed at the periphery of theelectrode pads, wherein conductive particles are metallically bonded tothe electrode pads.

Also, according to the present invention, there is provided a method ofmanufacturing a bumpless semiconductor device, comprising the followingsteps (a) and (b):

(a) a step of causing conductive particles to be electrostaticallyadsorbed onto one face of a flat plate; and

(b) a step of overlaying the surface of the plate having the adsorbedconductive particles on the surface of electrode pads of a bumplesssemiconductor device which is provided with the electrode pads on thesurface thereof and with a passivation film at the periphery of theelectrode pads, and ultrasonically welding this assembly, so that theconductive particles are metallically bonded and transferred from theflat plate to the electrode pads.

Furthermore, according to the present invention, there is provided aconnected structure, wherein this bumpless semiconductor device and acircuit board are joined by an insulating adhesive material so thatconductive particles metallically bonded with the connecting pads ofthis bumpless semiconductor device may contact the connection terminalsof the circuit board.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic cross-sectional view of a bumplesssemiconductor device according to the present invention;

FIGS. 2( a) to 2(d) are process diagrams for manufacturing a bumplesssemiconductor device and connected structure according to the presentinvention;

FIG. 3 is a diagram illustrating a prior art mode of connecting an ICchip and a circuit board;

FIG. 4 is a diagram illustrating a prior art mode of connecting an ICchip and a circuit board; and

FIG. 5 is a diagram illustrating a prior art mode of connecting an ICchip and a circuit board.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is further described in detail below withreference to the drawings.

FIG. 1 is an example in which a bumpless semiconductor device accordingto the present invention is applied to an IC chip. This IC chip 1 has abumpless construction in which electrode pads 2 made of for examplealuminum are provided at the surface thereof and a passivation film 3whose surface position level is higher than the surface position levelof the electrode pads 2 is provided at the periphery of the electrodepads 2. Also, conductive particles 4 are metallically bonded to theelectrode pads 2. Consequently, the connection reliability between theelectrode pads 2 and the conductive particles 4 rivals that of bumpsformed on a conventional IC chip as shown in FIG. 3 to FIG. 5.Furthermore, when metallic bonding of the conductive particles 4 to theelectrode pads 2 is effected, metallic bonding can be achieved by acomparatively low-cost technique such as ultrasonic welding, instead ofthe conventional complex and high-cost method of bump forming. Besides,the connection reliability between the conductive particles 4 and theconnection terminals of the circuit board (connected element) iscomparable with the conventional anisotropic conductor connectionmethod, since connection is achieved by the presence of conductiveparticles 4.

According to the present invention, metallic particles comprising solderparticles, nickel particles or other particles, or composite particlesin which a metallic plating layer of, for example, nickel or gold isformed on the surface of a resin particle (core) made of, for example,benzoguanamine or the like may be employed as the conductive particles4. Of these, use of composite particles with a resin particle corecapable of moderating stress applied to the connected portion ispreferred.

Regarding the particle diameter of the conductive particles 4,preferably at least some of the conductive particles 4 that aremetallically bonded are of a size such as to project to the outsidebeyond the surface of the passivation film 3. Specifically, preferablythey are larger than the difference of the surface levels of thepassivation film 3 and the electrode pads 2. In this way, occurrence ofshort-circuiting at the scribe lines can be suppressed and theconnection reliability with respect to the element to be connected(circuit board) can be improved. In this case, although the particlediameter of the conductive particles 4 may be made larger than thediameter of the electrode pads 2 in a range such that they are capableof metallic bonding with the electrode pads 2. Preferably, in order tosuppress short-circuiting between the conductive particles 4 in thelateral direction more effectively, the particle diameter of theconductive particles 4 is made smaller than the diameter of theelectrode pads 2. Specifically, the particle diameter of the conductiveparticles 4 is preferably between 1 and 50 μm and even more preferablybetween 3 and 40 μm in the case of metallic particles; in the case of acomposite particles, the diameter of the resin particles is preferably 1to 50 μm and even more preferably between 3 and 40 μm and the thicknessof the metallic plating layer is preferably between 10 nm and 1 μm, oreven more preferably between 15 nm and 1 μm.

Preferably, in order to reduce contact resistance, a thin gold platinglayer of thickness between about 5 nm and 0.5 μm is formed as theoutermost layer of the conductive particles 4.

As specific constructions of the IC chip 1, electrode pads 2 andpassivation film 3 in the embodiment of FIG. 1, prior art constructionsmay be respectively employed.

Next, each step of a method of manufacturing a bumpless semiconductordevice (IC chip) according to the present invention will be described.

Step (a)

As shown in FIG. 2( a), first of all, conductive particles 4 asdescribed above are electrostatically adsorbed onto one face of a flatplate 21 such as a flat glass plate. In this case, in order to moreeffectively transfer the conductive particles during ultrasonic weldingin step (b), they are preferably adsorbed as a single layer. As thetechnique for adsorbing the conductive particles 4 electrostaticallyonto the flat plate 21, the surface of the flat plate 21 may beelectrostatically charged by wiping it with a polyester cloth or thelike and the conductive particles 4 then dispersed over the surface.Conductive particles that have not been adsorbed can be removed bytilting or turning over the flat plate 21 or by gently vibrating theflat plate 21.

Step (b)

Next, as shown in FIG. 2( b), the surface of the flat plate 21 ontowhich the conductive particles have been adsorbed is overlaid with theelectrode pad surface 2 of an IC chip 1 provided with electrode pads 2on the surface thereof and a passivation film 3 at the periphery of theelectrode pads 2 and ultrasonic welding is performed preferably from thedirection of the arrow (FIG. 2( c)). In this way, the conductiveparticles 4 can be transferred from this flat plate 21 to the electrodepads 2 by metallic bonding with the electrode pads 2. It should be notedthat transfer of the conductive particles 4 onto the passivation film 3,which is an insulating film, does not take place, since the conductiveparticles 4 cannot perform metallic bonding therewith.

As example conditions for welding, there may be mentioned application ofa frequency between 10 and 100 KHz with a pressure between 1 and 100 MPa(per electrode pad) for between 0.1 and 20 sec. As a specific example ofequipment that may be employed, the Ultrasonic Micro Welding System(SH40MP, manufactured by ULTAX Inc) can be given.

Step (c)

If necessary, any conductive particles 4 that have become attached tothe passivation film 3 may then be removed by transferring ontocommercially available tacky adhesive tape or blowing off by airblowprocessing, to obtain the bumpless semiconductor device (IC chip) 1shown in FIG. 2( d).

With the bumpless semiconductor device (IC chip) 1 shown in FIG. 2( d),a connected structure having high connection reliability can beachieved. Specifically, a connected structure (FIG. 2( e)) may bepresented in which a bumpless semiconductor device 1 and a circuit board5 are joined by a known insulating adhesive material 7 in the form of afilm or paste so that conductive particles 4 that are metallicallybonded with the connecting pads 2 may contact the connecting terminals 6of the circuit board 5.

EXAMPLES

A specific description of the present invention is given below withreference to Examples thereof.

Examples 1 to 8 and Comparative Examples 1 to 4

After wiping one face of a flat glass plate with polyester cloth, theconductive particles of Table 1 were distributed and adsorbed onto thissurface. The excess conductive particles were removed by tilting theglass plate and vibrating it gently. In the case of practical example 6,metallic particles provided with an Au plated layer on the surface of anNi core were employed as the conductive particles but, in the otherpractical examples and the comparative examples, composite particles inwhich an Ni plated layer and Au plated layer were formed on the surfaceof benzoguanamine (core resin particles) were employed.

The conductive particles adsorption face of this flat glass plate wasoverlaid with the electrode pad formation face of a 10 mm square IC chipprovided with 500 of aluminum electrode pads on one face thereof in apitch of 80 μm, and subjected to an ultrasonic welding treatment(frequency 10, 50 or 100 kHz, pressure 49 MPa, treatment time 10 sec),using an ultrasonic welding device (Ultrasonic Micro Welding System(SH40MP, manufactured by ULTAX Inc), from the side of the flat glassplate. The conductive particles were thereby transferred by metallicbonding to the electrode pads of the IC chip. Excess conductiveparticles adhering to the passivation film were blown away by airblowtreatment, to obtain the bumpless semiconductor device (IC chip) shownin FIG. 1.

TABLE 1 Conductive particles Ultrasonic Core resin Ni plating Au platingwelding particle diameter thickness thickness frequency (μm) (μm) (nm)(kHz) Ex. 1 5 0.15 20 50 Ex. 2 1 0.15 20 50 Ex. 3 50 0.15 20 50 Ex. 4 50.15 10 50 Ex. 5 5 0.15 1000 50 Ex. 6 10 — 20 50 Ex. 7 5 0.15 20 10 Ex.8 5 0.15 20 100 Comp. EX. 1 0.5 0.15 10 50 Comp. EX. 2 55 0.15 20 10Comp. EX. 3 5 0.15 20 50 Comp. EX. 4 5 0.15 1100 50

Next, the electrode pads of the bumpless semiconductor device obtainedwere positionally aligned with the connecting terminals (circuit pattern(80 μm pitch) obtained by gold plating onto copper of height 8 μm) of apolyimide circuit board of thickness 25 μm, a thermo-setting epoxyinsulating adhesive film (obtained by removing the conductive particlesfrom anisotropic conductive adhesive film (FP16613, manufactured by SonyChemicals) was sandwiched therebetween, and the assembly wasthermo-compression bonded under the conditions of temperature 190° C.,pressure 1960 kPa, and 10 sec, to obtain a connected structure.

When the connected structure obtained was subjected to a thermal shocktest (1000 cycles) between −55° C. and 125° C., the connected structureusing the bumpless semiconductor devices of practical examples 1 to 5and 7 to 8 displayed excellent connection reliability, the rise inresistance being in each case no more than 10 mΩ. Also, the rise inresistance of the connected structure employing the bumplesssemiconductor device of Example 6 was about 200 mΩ, which is a levelthat presents no practical problems.

In contrast, in the case of the connected structure employing thebumpless semiconductor device of comparative example 1, the rise inresistance exceeded 1 Ω, because the core resin particle diameter wastoo small. In the case of the connected structure employing the bumplesssemiconductor device of comparative example 2, the core resin particlediameter was too large, so some of the particles appeared that could notbe carried on the pads, causing the initial resistance value to becomelarge, with the result that this connected structure was unsuitable foruse. In the case of the connected structure using the bumplesssemiconductor device of comparative example 3, the thickness of themetallic plating layer at the surface of the core resin particles wastoo thin, so electrode pads appeared where no conductive particles weretransferred, causing the initial resistance value to become high, withthe result that this connected structure was unsuitable for use. Also,in the case of the connected structure using the bumpless semiconductordevice of comparative example 4, the thickness of the metallic platinglayer at the surface of the core particles was too thick, so theconductive particles coagulated, generating short-circuits.

INDUSTRIAL APPLICABILITY

According to the present invention, when a semiconductor device such asan IC chip is connected with a circuit board by the flip-chip method,the IC chip and the circuit board can be connected with high reliabilityand low cost while suppressing short-circuits, reducing the connectioncost, suppressing stress concentrations in the joints and reducingdamage to the IC chip or circuit board, without forming bumps on thesemiconductor device.

1. A method of manufacturing a bumpless semiconductor device, comprisingthe following steps (a) and (b): (a) a step of causing conductiveparticles to be electrostatically adsorbed onto one face of a flatplate; and (b) a step of overlaying the surface of the plate having theadsorbed conductive particles on the surface of electrode pads of abumpless semiconductor device which is provided with the electrode padson the surface thereof and with a passivation film at the periphery ofthe electrode pads, and ultrasonically welding this assembly, so thatthe conductive particles are metallically bonded and transferred fromthe flat plate to the electrode pads.
 2. The method of manufacturing abumpless semiconductor device according to claim 1, further comprisingforming a metallic plating layer on a surface of resin particles,wherein the conductive particles are composite particles.
 3. The methodof manufacturing a bumpless semiconductor device according to claim 2,wherein a diameter of the resin particles is between 1 and 50 μm and athickness of the metallic plating layer is between 10 nm and 1 μm. 4.The method of manufacturing a bumpless semiconductor device according toclaim 2, wherein at least some of the conductive particles that aremetallically bonded project to the outside of the surface of thepassivation film.